Quoting Jason Gunthorpe (2019-07-17 04:39:56) > On Tue, Jul 16, 2019 at 03:45:13PM -0700, Stephen Boyd wrote: > > The hwrng_fill() function can run while devices are suspending and > > resuming. If the hwrng is behind a bus such as i2c or SPI and that bus > > is suspended, the hwrng may hang the bus while attempting to add some > > randomness. It's been observed on ChromeOS devices with suspend-to-idle > > (s2idle) and an i2c based hwrng that this kthread may run and ask the > > hwrng device for randomness before the i2c bus has been resumed. > > You mean the TPM here right? In my case yes, but in general it isn't the TPM. > > Should we be more careful in the TPM code to check if the TPM is > suspended before trying to use it, rather than muck up callers? > Given that it's not just a TPM issue I don't see how checking in the TPM is going to fix this problem. It's better to not try to get random bytes from the hwrng when the device could be suspended.
